Process for improving chrome tanned leather



United States Patent 2,998,294. PROCESS FOR IMPROVING CHROMETANNED.LEATHER Charles Thomas Locke, Plymouth, Wis., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware NoDrawing. Filed Aug. 7, 1959, Ser. No.832,181

12 Claims. (Cl. 8-9.4;21)

The invention relates to a novel process for improving chrome tannedleather. andvparticularly to a process for filling and lumping fullychrome tannedleather.

It is an objectof this invention to=provide a new and improved processfor improving the quality of fully chrome tanned leather. Another objectis, to provide a process for filling and plumping chrome tanned leather,particularly to provide a leather which is full, dense, smooth,tight-grained and has improved. body. Other objects are to advance theart. Still other objects will appear hereinafter.

The above and other objects may be accomplished inv accord with thisinvention which involves the process which comprises impregnating fullychrome tanned leather at a temperature of from about 80 F. to about 120F. with anaqueous solution ofa water-soluble inorganic acidic salt of ametalof the group consisting of aluminum, zirconium and zinc in anamountto provide from about 0.5% to about 2.5% by weight of said saltbased on the leather, then impregnating the leather at a temperatureoffrom about 75 F. to about 135 F. with an aqueous solution ofdi(methoxymethyl)dimethylolurea in an amount to provide from about 1.5%to about 30% by weight of said urea based on the leather, and thenimpregnating the leather at a temperature of from about 80 F. to about135 F. with an aqueous solution of a water-soluble inorganic acidic saltof a metal of the, group consisting of aluminum, zirconium and zinc inan amount to provide from about 0.5 to about 10% by weight of the acidicsalt based on the leather.

Such process is essentially a filling and plumping process and is notatanning or retanning process. By means of the process of thisinvention, the finished leather. is rendered noticeably full and dense.leather is rendered very smooth and tight whereby it providesanexcellent surface for snufiing or butfingtoobtain a nap or--a buckfinish. The solidity of the, leather, is. so: greatly improved thatcowhide; can be made to approach, the leather qualities of high gradecalfskin.

p The process of this; invention may be applied advantageously to. anytype of chrome; tanned leather including split and shaved side leather,grain and suede and the like. The leather may be obtained from goatskin,cowhide, sheepskin, etc., and the product may be used for shoe, case,glove, and garment leathers. The leather to be treated by this processshould be properly fully chrome tannedl. If the original chrome tan didnot penetrate sufficiently, leaving untanned spots on the flesh sideafter splitting, the leather should be retanned in the usual manner withbasic chromic sulfate.

The salts which may be employed in accord with this invention are the:water-soluble, inorganic acidic salts of used because they discolor theleather, but can be used if;

the leather is. to be dyed dark shades. Preferred salts are those ofaluminum and zirconium, particularly aluminum sulfate and zirconiumsulfate.

The grain ofthe "ice Di(methoxymethyl)dimethylolurea is. a knowncomposition which hasbeen employedfor imparting creaseresis'tantproperties totextiles. .Its properties and preparation are described byEtzel: in Patent 2,825,710.

Theprocessof this invention comprises the three steps of. treating thechrome tannedleather with the acidic salt,

subsequently treating -i-t, with. the di(methoxymethyl)dithe salt basedon the leather, preferably from about 0.5% to about 2.0%. The aqueoussolution should containthe salt in a concentration of from about 0.5 toabout 20% by weight, preferably from about 0.75% to about 10%. Thequantity of the acidic salt based on the leather employed in this stepis dependent upon the degree of penetration of thedi(methoxymethyl)dimethylolurea desired and the amount of fillingdesired in the leather. The lower amount of the acidic, salt will beused where it is desired that the final leather will have the maximumamount of filling and thickness. The higher amount of acidic salt willbe employed when it is desired to impart a minimum advantageous amountof filling in the final leather. This first step of the process ofthisinvention and theamount of acidic salt employed therein areessential to control the degree of penetration and of retention of thedi(methoxymethyl)dimethylolurea in the leather. Thedi(methoxymethyl)dimethylolurea is insolubilized by the acidic salts. Ifthe leather is not first impregnated with the acidic salt or ifmaterially less than 0.5% thereof is employed, thedi(methoxymethyl)dimethylolurea will completely penetrate the leatherbut, when the final treatment with the acidic salt is carried out, onlysurface fixa tion of the di(methoxymethyl)dimethylolurea occurs and thatremaining in the interior ofthe leather is washed out during subsequentdrumming procedures, whereby the desired filling and plumping effectswill not be accomplished throughout the leather. On the. other hand, ifmaterially more than about 2.5% of the acidic salt is employed in thisfirst step, the di(methoxymethyl)dimethylolurea will become fixed at thesurface of the leather before it is able to penetrate into the interiorof the leather, whereby the desired filling and plumping effectthroughout the leather will not be obtained.

The chrome tanned leather, containing the acidic salt from the firststep, is impregnated withfrom about 1.5% to about 30% by weight of thedi(methoxymethyl)dimethylolurea by drumming the leather with an aqueoussolution thereof. The amount of the di(methoxymethyl) dirnethylolureaemployed will be directly proportional to the amount of plumping andfilling obtained. Materially less than about 1.5% based on the leathergives inadequate filling and plumping, and materially more than 30% isunnecessary for obtaining maximum filling and plumping. The preferredamount of di(methoxymethyl)dimethylolurea is from about 5% to about 6%by weight based on the weight of the leather taken. The aqueous solutionemployed in this step usually will contain thedi(methoxyrnethyl)dimethylolurea in a concentration of from about 10% toabout by weight, preferably from about 20% to about 70%. The leather isimpregnated with such solution by the usual drumming procedure which maybe carried out at a temperature at from about 75 F. to about 135 F.,preferably from about F. to about F. The usual drumming time will varyfrom about one hour at the lower temperatures to about 10 to 40 minutesat the higher temperatures. The most preferred time and temperature willbe about 30 minutes at about 130 F.

The leather, impregnated with the di(methoXymethyD- dimethylolurea, mustbe again impregnated with an aqueous solution of an acidic salt of thecharacter employed in the first step, which acidic salt may be the sameor different from that employed in the first step. In this third step,the acidic salt employed will be from about 0.5% to about 10% by weightbased on the weight of the leather taken, preferably from about 1.5% toabout 2.0%. The aqueous solution employed will contain the acidic saltin a concentration of from about 0.5% to about 20% by weight, preferablyfrom about 10% to about 15%. Again, the impregnation is carried out bydrumming, usually at a temperature of from about 80 F. to about 135 F.,preferably from about 100 F. to about 110 F. The time of drumming mayvary from about 10 minutes to about 30 minutes. This third step isrequired for complete insolubilization of thedi(methoxymethyl)dimethylolurea and optimum plumping and filling of theleather. When a large amount of the acidic salt is used in the firststep and a small amount of di(methoxymethyDdimethylolurea is employed inthe second step, only a small amount of acidic salt is necessary in thethird step. However, excessive amounts of the acidic salt in the thirdstep is not objectionable and, to the extent that it penetrates theleather, it provides additional filling effects.

After the final impregnation with the acidic salt, the leather thatresults is finished off by rinsing and it may be treated with softeningagents and/ or fat liquor in the normal manner. If white leather isdesired, it may be treated with a white pigment, such as titaniumdioxide,

and this may be done during the fat liquor procedure. If desired, acidor direct dyes may be used either prior to the process of this inventionor at any step of the process. When dyes are used, it is desirable totreat the chrome tanned leather with a neutral syntan after the firststep of this process, as this prevents undesired precipitation of dye bythe acidic salt and ensures that a level dyeing is obtained. The neutralsyntans are well known surface active agents employed for leveling dyesin leathers and are represented by neutral naphthalene syntan which is asulfonated naphthalene condensate synthetic retanning agent.

It is particularly advantageous to treat the leather, obtained by theprocess of this invention, with a mixture of a softener and a sulfonylchloride tanning agent. This treatment imparts a very desirablesoftening effect to the leather fibers. The preferred softeners areparaffin wax and petrolatum, and these agents are preferably employed asa dispersion in an aqueous solution of the alkali-metal sulfonates ofparafiin wax and petrolatum. These and other softener compositions, suchas fatty acid amides and alkyl biguanidines, are well known in the art.The sulfonyl chloride tanning agents are well known (I. Am. LeatherChemists Assoc. 44, pages 222, (1949)), and consist essentially ofincompletely chlorosulfonated hydrocarbon oils such as No. 40 white oil.These agents are commonly used as aqueous dispersions in the leather artto produce chamois type leathers. In softening the full, tight-grainedleather obtained by the novel process of this invention, the softenerand sulfonyl chloride tanning agents are mixed and used to drum theleather at from about 80 F. to about 130 F. for from about 30 minutes toabout 60 minutes. If desired, subsequent treatments with fat liquoringagents, such as neatsfoot oil, may be given to the leather to add adesired greasy feel.

In order to more clearly illustrate this invention, preferred modes ofcarrying it into elfect and advantageous results obtained thereby, thefollowing examples are 4 given in which the proportions are by weightexcept where specifically indicated otherwise.

Example 1 Chrome tanned cowhide leather from the splitting and shavingmachine is placed in a drum and retanned with basic chromium sulfate inthe usual manner to cover untanned spots on the fleshside aftersplitting.

The sides are rinsed and then treated with 2.0 percent aluminum sulfateand 75 percent water, based on the weight of the leather. The sides aredrummed 20 minutes at F. Then, 20 percent of the leather weight of a 10percent solution of neutral naphthalene syntan water is added and thesides are drummed for 20 minutes at 110 F. 27.5 percent of the leatherweight of a 20 percent solution of di(methoxylmethyl)dimethylolurea inwater is added and the sides are drummed 30 minutes at 110 F. Then, 20percent of a 10 percent solution of aluminum sulfate in water is addedand the sides are drummed for 20 minutes at 110 F. The sides are rinsedand fat liquored in the usual manner. A white pigment, titanium dioxide,is added with the fat liquor to produce a White leather. A cowhide shoeupper leather is produced which has an unusually smooth and tight grain.The leather is full and dense.

When the process is applied to chrome tanned goatskin and to chrometanned sheepskin for shoe and garment leathers, a full, dense leather isobtained.

When zinc sulfate is used in the above example, essentially the sameresults are obtained.

Example 2 Chrome tanned cowhide leather is placed in a drum and rinsedat F. Based on the weight of the leather, 1.5 percent of a dye, ResorcinBrown C. I. 234, 1.0 percent neutral naphthalene syntan, 1.0 percentaqueous ammonia (37.0%), and 75 percent water are added at 120 F. andthe sides are drummed for 30 minutes. Then, 5.0 percent of a 10-percentsolution of aluminum sulfate in water is added at 110 F. and the sidesare drummed 20 minutes. 27.5 percent of a 20-percent solution ofdi(methoxymethyl)dimethylolurea in water is added at 110 F. and thesides are drummed 30 minutes. Then 20 percent of a 10-percent solutionof aluminum sulfate in water is added at 110 F. and the sides aredrummed for 20 minutes. The sides are rinsed and fatliquored in theusual manner.

The leather is dried and staked in the usual manner and the grain isbufi'ed to obtain a. nap for a buck finish. The resultant leather has anunusually full and dense body with a fine nap.

In lieu of aluminum sulfate in the above example, aluminum chloride isused with essentially the same results.

Example 3 Rinse chrome tanned side leather in a drum, drain and add onthe weight of the leather 2 percent sodium chloride, 1.5 percentzirconium sulfate and 200 percent water. Drum 20 minutes at 100 F. Add8.6 percent on the Weight of the leather of a 68% by weight aqueoussolution of di(methoxymethyl) dimethylolurea and 20 percent water. Drum30 minutes at 100 F. Add 1.5 percent zirconium sulfate and 10 percentwater and drum 20 minutes at 100 F. Rinse for 20 nlinutes at F. anddrain. Then, add 3 percent of a sulfonyl chloride tanm'ng agent(incompletely chlorosulfonated No. 40 white oil dispersed withaLlpha-pinene and a polyethylene oxide adduct of a fatty alcohol) and 3percent of a softener (a dispersion of parafiin wax and petrolatum in anaqueous solution of the sodium sulfonates of paraffin and petrolatum)and percent water and drum for 30 minutes at 130 F. Drain and add 1percent neatsfoot oil and 1 percent of sulfated neatsfoot oil at 130 F.with 150 percent water and drum 30 minutes.

After drying, this leather is very light in color and i8 a good qualitywhite leather. It is dense and has avery fine break.

It will be understood that the preceding examples have been given forillustrative purposes solely and that this invention is not limited tothe specific embodiments described therein. On the other hand, it willbe apparent to those skilled in the art, subject to the limitations setforth in the general description, that many variations and modificationscan be made in the materials, proportions, conditions and techniquesemployed without departing from the spirit or scope of this invention.

From the preceding description, it will be apparent that this inventionprovides a novel process for greatly improving the quality of chrometanned leather. Particularly, it provides a finished leather which isnoticeably more full and dense and has a grain which is very smooth andtight, whereby the treated leather is useful for a wide variety ofpurposes for which the original chrome tanned leather is not adapted.Accordingly, it is believed that this-invention constitutes a veryvaluable advance in and contribution to the art.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from about80 F. to about 120 F. with an aqueous solution of a water-solubleinorganic acidic salt of a metal of the group consisting ofaluminum,zirconium andzinc in an amount to provide from about 0.5% to about 2.5%by weight of said salt based on the leather, then impregnating theleather at a temperature of from about 75 F. to about 135 F. with anaqueous solution of di(methoxymethyl) dimethylolurea in an amount toprovide from about 1.5% to about 30% by weight of said urea based on theleather, and then impregnating the leather at a temperature of fromabout 80 F. to about 135 F. with an aqueous solution of a water-solubleinorganic acidic salt of a metal of the group consisting of aluminum,zirconium and-zinc in an amount to provide from about 0.5% to about 10%by.

weight of the acidic salt based on the leather.

2. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from about80 F. to about 120 F. with an aqueous solution of a water-solubleinorganic acidic salt of a metal of the group consisting of aluminum,zirconium and zinc in an amount to provide from. about 0.5 to about 2.5%by weight of said salt based on the leather, then impregnating theleather at a temperature of from about 75 F. to about 135 F. with anaqueous solution of di(methoxymethyl) dimethylolurea in an amount toprovide from about to about 6% by weight of said urea based on theleather, and then impregnating the leather at a temperature of fromabout 80 F. to about 135 F. with an aqueous solution of a water-solubleinorganic acidic salt of a metal of the group consisting of aluminum,zirconium and zinc in an amount to provide from about 0.5 to about 10%by weight of the acidic salt based on the leather.

3. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from about100 F. to about 110 F. with an aqueous solution of a water-solubleinorganic acidic salt of a metal of the group consisting of aluminum,zirconium and zinc in an amount to provide from about 0.5 to about 2.5%by weight of said salt based on the leather, then impregnating theleather at a temperature of from about 100 F. to about 130 F. with anaqueous solution of di(methoxymethyl)dimethylolurea in an amount toprovide from about 5% to about 6% by weight of said urea based on theleather, and then impregnating the leather at a temperature of fromabout 100 F. to about 110 F. with an aqueous solution of a water-solubleinorganic acidic salt of a metal of the group consist- 6 ing ofaluminum, zirconium and zinc in an amount to provide from about 1.5% toabout 2.0% byweight of the acidic salt based on the leather;

4. Theprocess forimproving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from aboutF. to about 120 F. with an aqueous solution of awater-soluble inorganicacidic salt of aluminum in an amount to provide from about 0.5% to about2.5% by weight of said salt based on the leather, then impregnating theleather at a temperature of from about 75 -F. to about 135 F. with anaqueous solution of di(rnethoxymethyl) dimethylolurea in an amount toprovide from about 1.5% to about 30% by weight of said urea based on theleather, and then impregnatingthe leather at a temperature of from about80 F. to about 135 F. with an aqueous solution of a water-solubleinorganic acidic salt of aluminum in anamount to provide from about 0.5to about 10% by weight of the acidic salt based on the leather.

5. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from about80 F. to about 120 F. with an aqueous solution of a water-solubleinorganic acidic salt of aluminum in an amount to provide from about0.5% to about 2.5 by weight of said salt based on the leather, thenimpregnating the leather at a temperature of from about 75 F. to'about135 F. with an aqueous solution of di(methoxymethyl)dimethylolurea in anamount to provide fromabout 5% to about 6% by weight of said urea basedon the leather, and then impregnating the leather at a temperature offrom about 80 F. to aboutL135 F. with an aqueous solution of aWater-soluble inorganic acidic salt of aluminum in an' amount to providefrom about, 0.5 to about 10% by weight of the acidic salt based on theleather.

6. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from about80 F. to about 120 F. with an aqueous solution of aluminum sulfate in anamount to provide from about 0.5 to about 2.5 byweight of said aluminumsulfate based on the leather, then impregnating the leather at atemperature of from about 75 F. to about 135 with an aqueous solution ofd-i(methoxymethyl)dimethylolurea in an amount to provide from about 1.5to about 30% by weight of said urea based on the leather, and thenimpregnating the leather at a temperature of from about 80 F. to about135 F. with an aqueous solution of aluminum sulfate in an amount toprovide from about 0.5% to about 10% by weight of the aluminum sulfatebased on the leather.

7. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leathor at a temperature of from aboutF. to about F. with an aqueous solution of aluminum sulfate in an amountto provide from about 0.5 to about 2.5 by Weight of said aluminumsulfate based on the leather, then impregnating the leather at -atemperature of from about 100 F. to about F. with an aqueous solution ofdi(methoxymethyl)dimethylolurea in an amount to provide from about 5% toabout 6% by weight of said urea based on the leather, and thenimpregnating the leather at a temperature of from about 100 F. to about110 -F. with an aqueous solution of aluminum sulfate in an amount toprovide from about 1.5% to about 2.0% by weight of the aluminum sulfatebased on the leather.

8. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from about100 F. to about 110 F. with an aqueous solution of aluminum chloride inan amount to provide from about 0.5% to about 2.5 by weight of saidaluminum chloride based on the leather, then impregnating the leather ata temperature of from about 100 F. to about 130 F. with an aqueoussolution of di(methoxymethyl)dimethylolurea in an amount to provide fromabout to about 6% by weight of said urea based on the leather, and thenimpregnating the leather at a temperature of from about 100 F. to about110 F. with an aqueous solution of aluminum chloride in an amount toprovide from about 1.5% to about 2.0% by weight of the aluminum chloridebased on the leather. 7 9. The process for improving chrome tannedleather which com-prises impregnating fully chrome tanned leather at atemperature of from about 80 F. to about 120 F. with an aqueous solutionof a water-soluble inorganic acidic salt of zirconium in an amount toprovide from about 0.5% to about 2.5% by weight of said salt based onthe leather, then impregnating the leather at a temperature of fromabout 75 F. to about 135 F. with an aqueous solution ofdi(methoxyrnethyl)dimethylolurea in an amount to provide from about 1.5%to about 30% by weight of said urea based on the leather, and thenimpregnating the leather at a temperature of from about 80 F. to about135 F. with an aqueous solution of a Water-soluble inorganic acidic saltof zirconium in an amount to provide from about 0.5% to about 10% byweight of the acidic salt based on the leather.

10. The process for improving chrome tanned leather Which comprisesimpregnating fully chrome tanned leather at a temperature of from about100 F. to about 110 F. with an aqueous solution of a water-solubleinorganic acidic salt of zirconium in an amount to provide from about0.5 to about 2.5% by weight of said salt based on the leather, thenimpregnating the leather at a temperature of from about 100 F. to about130 F. with an aqueous solution of di(methoxymethyl)dimethylolurea in anamount to provide from about 5% to about 6% by Weight of said urea basedon the leather, and then impregnating the leather at a temperature offrom about 100 F. to about 110 F. with an aqueous solution of awater-soluble inorganic acidic salt of zirconium in an amount to providefrom about 1.5 to about 2.0% by weight of the acidic salt based on theleather.

11. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from about80 F; to about 120 F. with an aqueous solution of zirconiumsulfate in anamount to provide from about 0.5% to about 2.5% by weight of saidzirconium sulfate based on the leather, then impregnating the leather ata temperature of from about F. to about 135 F. with an aqueous solutionof di(methoxymethyl) dimethylolurea in an amount to provide from about1.5% to about 30% by weight of said urea based on the leather, and thenimpregnating the leather at a temperature of from about F. to about 135F. with an aqueous solution of zirconium sulfate in an amount to providefrom about 0.5 to about 10% by weight of the zirconium sulfate based onthe leather.

12. The process for improving chrome tanned leather which comprisesimpregnating fully chrome tanned leather at a temperature of from aboutF. to about F. with an aqueous solution of zirconium sulfate in anamnount to provide from about 0.5% to about 2.5% by weight of saidzirconium sulfate based on the leather, then impregnating the leather ata temperature of from about 100 F. to about F. with an aqueous solutionof di( methoxyrnethyl)dimethylolurea in an amount to provide from about5% to about 6% by Weight of said urea based on the leather, and thenimpregnating the leather at a temperature of from about 100 F. to about110 F. with an aqueous solution of zirconium sulfate in an amount toprovide from about 1.5% to about 2.0% by weight of the zirconium sulfatebased on the leather.

OFlaherty et al.: Chemistry and Technology of Leather, vol. 2, ReinholdPub. Corp., N.Y., 1958, p. 476.

1. THE PROCESS FOR IMPROVING CHROME TANNED LEATHER WHICH COMPRISESIMPREGNATING FULLY CHROME TANNED LEATHER AT A TEMPERATURE OF FROM ABOUT80*F. TO ABOUT 120*F. WITH AN AQUEOUS SOLUTION OF A WATER-SOLUBLEINORGANIC ACIDIC SALT OF A METAL OF THE GROUP CONSISTING OF ALUMINUM,ZIRCONIUM AND ZINC IN AN AMOUNT TO PROVIDE FROM ABOUT 0.5% TO ABOUT 2.5%BY WEIGHT OF SAID SALT BASED ON THE LEATHER, THEN IMPREGNATING THELEATHER AT A TEMPERATURE OF FROM ABOUT 75*F. TO ABOUT 135*F. WITH ANAQUEOUS SOLUTION OF DI(METHOXYMETHYL) DIMETHYLOLUREA IN AN AMOUNT TOPROVIDE FROM ABOUT 1.5% TO ABOUT 30% BY WEIGHT OF SAID UREA BASED ON THELEATHER, AND THEN IMPREGNATING THE LEATHER AT A TEMPERATURE OF FROMABOUT 80*F. TO ABOUT 135*F. WITH AN AQUEOUS SOLUTION OF A WATER-SOLUBLEINORGANIC ACIDIC SALT OF A METAL OF THE GROUP CONSISTING OF ALUMINUM,ZIRCONIUM AND ZINC IN AN AMOUNT TO PROVIDE FROM ABOUT 0.5% TO ABOUT 10%BY WEIGHT OF THE ACIDIC SALT BASED ON THE LEATHER.